Superhydrophobic poly(dimethylsiloxane) and methods for making the same

ABSTRACT

A hydrophobic coating having a contact angle of at least about 150 degrees is disclosed herein, which coating comprises: a polymer substrate comprising a first linker incorporated therein at a specified surface density of from about 3×10 −4  to about 9×10 −8  units per nm 2 ; a first polymer layer in contact with said first linker; a second linker in contact with said first polymer layer; and a second polymer layer in contact with said second linker. Also disclosed herein are methods for producing the hydrophobic coating. This hydrophobic coating is useful for making microfluidic devices having a hydrophobic coating on the microfluidic channels, as well as other uses in the field of microfluidics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/529,217, filed Aug. 31, 2009, which is the U.S. National Stage ofPatent Cooperation Treaty Application No. PCT/CN2008/071944 filed onAug. 11,2008, both of which are hereby incorporated by Reference intheir entirety.

FIELD

Disclosed herein is a hydrophobic coating having a contact angle of atleast about 150 degrees and methods for making the same. Also disclosedare uses for the hydrophobic coating such as in microfluidic devices.

BACKGROUND

Superhydrophobic surfaces have many important applications in naturallyoccurring systems and in artificial devices, which applications haveinspired intensive research activities with regard to the preparationmethods and theoretical modeling (Zhang, X., et al., J. Mater. Chem.2008, 18, 621-633, Li, X. M., et al., Chem. Soc. Rev. 2007, 36,1350-1368, Genzer, J., et al., Biofouling 2006, 22, 339-360, Sun, T. L.,et al., Ace. Chem. Res. 2005, 38, 644-652). It is of particular interestto create superhydrophobic surface inside a microfluidic channel. Thisis important in a number of applications and fundamental studies, suchas fluidic flow control in microfluidic devices (Gau, H., et al.,Science 1999, 283, 46-49, Takei, G., et al., Lab Chip 2007, 7, 596-602)and fluidic behavior study (Atencia, J., et al., Nature 2005, 437,648-655). Poly(dimethyl siloxane) (PDMS) is the most commonly usedmaterial in the fabrication of microfluidic devices (Whitesides, G. M.Nature 2006, 442, 368-373, Psaltis, D., et al., Nature 2006, 442,381-386).

SUMMARY

In general, disclosed herein are superhydrophobic coatings as well asmethods for preparing the superhydrophobic coatings. The methodsdisclosed herein utilize a relayed surface-initiated polymerization(SIP) strategy to produce superhydrophobic surfaces. It has been foundthat an ultra low initiator density can be used to prepare asuperhydrophobic surface. Three factors are optimized to achieve thesuperhydrophobic surfaces. These factors are the ultra low initiatordensity, the relayed SIP strategy, and a hydrophobic monomer asdisclosed herein.

Disclosed herein is a hydrophobic coating having a contact angle of atleast about 150 degrees, which coating comprises:

a polymer substrate comprising a first linker incorporated therein at aspecified surface density of from about 3×10⁻⁴ to about 9×10⁻⁸ units pernm²;

a first polymer layer in contact with said first linker;

a second linker in contact with said first polymer layer; and

a second polymer layer in contact with said second linker.

Also disclosed is a hydrophobic coating having a contact angle of atleast about 150°, which coating comprises:

-   -   a poly(dimethyl) siloxane substrate comprising a first linker        incorporated therein at a surface density of from about 3×10⁻⁴        to about 9×10⁻⁸ units per nm²;    -   a polyether layer in contact with said first linker;    -   a second linker in contact with said polyether layer; and    -   a fluorinated polymer layer in contact with said second linker.

Also disclosed is a method of making a hydrophobic coating having acontact angle of at least about 150 degrees, said method comprising:

1) providing a polymer substrate wherein a first linker is incorporatedinto the substrate at a surface density of from about 3×10⁻⁴ to about9×10⁻⁸ units per nm²;

2) contacting a monomer with said first linker under first polymerizingconditions to provide a first polymer layer bound to the polymersubstrate through the first linker;

3) contacting a second linker with said first polymer layer underreaction conditions to provide a reactive surface; and

4) contacting a monomer with said reactive surface under secondpolymerizing conditions to provide the hydrophobic coating.

Also disclosed is a method for making a hydrophobic coating having acontact angle of at least about 150 degrees, said method comprising:

1) polymerizing a mixture comprising apoly(dimethyl-methylvinylsiloxane) prepolymer,poly(dimethyl-methylhydrogensiloxane) precursors andundec-10-enyl-2-bromo-2-methylpropanoate, under thermal conditions toform a polymer substrate;

2) contacting oligo(ethylene glycol) methacrylate with said polymersubstrate under first polymerizing conditions to provide a first polymerlayer bound to the polymer substrate through theundec-10-enyl-2-bromo-2-methylpropanoate;

3) contacting 2-bromoisobutyryl bromide with said first polymer layerunder reaction conditions to provide a reactive surface; and

4) contacting 1H,1H,2H,2H-perfluorodecyl methacrylate with said reactivesurface under second polymerizing conditions to provide the hydrophobiccoating.

It is contemplated that the superhydrophobic coating disclosed hereinmay be produced using more than two iterations of the SIP strategy toachieve a suitable surface topography. In addition, depending on themonomers used, it is possible that the second polymer layer be in directcontact with the first polymer layer thus omitting the second linker.

In some embodiments, the superhydrophobic surface is used to produce amicrofluidic device, comprising at least one channel disposed thereon.Microfluidic devices comprising the hydrophobic surface disclosed hereinare useful in the area of biotechnology, e.g., “lab-on-a-chip”. Sincemicrofluidic technology is based on the manipulation of liquid flowthrough microfabricated channels, the ability to control the liquid flowis desired. In addition, the in situ modification of an internal wall ofa microfluidic channel made from iPDMS can be performed and used asmicrofluidic devices.

In some embodiments, the hydrophobic coating disclosed herein is proteinresistant (Gudipati, C. S., et al., Langmuir 2005, 21, 3044-3053). Thus,in some embodiments, the hydrophobic coating is used to provide articleswhich are protein resistant. This enables the production of variousprotein resistant articles, such as microfluidic devices, which can beused for analytical and/or purification assays, and the like.

In addition, many objects such as boats and marine monitoring devices,which are continually exposed to water require a protective coating topreserve their utility. Therefore, these methods can also be applied toprovide marine anti-fouling materials (Genzer, J., et al., Biofouling2006, 22, 339-360). In some embodiments, the hydrophobic coating is usedto produce articles which are marine antifoulable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relayed surface-initiated polymerization (relayed SIP)from the initiator integrated PDMS (iPDMS) of ultra low initiatordensity (S1 stands for step 1). The inset shows a schematic of themicrostructure of the polymer achieved by the second SIP.

FIG. 2, panels (A)-(I), show scanning electron microscope and contactangle images of the initiator integrated PDMS (iPDMS) surfaces after therelayed surface-initiated polymerization (SIP) strategy (A)-(F) andafter only one iteration of the SIP strategy (G)-(I). Panels (A) and (B)show the surface morphology of the iPDMS with a feed initiator ratio of0.5 (0.5iPDMS). Panel (C) shows a water droplet on the 0.5iPDMS surface.Panels (D) and (E) show the surface morphology of the iPDMS with a firstlinker ratio of 10:1:10⁻³ (10⁻³iPDMS). Panel (F) shows a water dropleton the 10⁻³iPDMS surface. The sliding angle was determined to be about1.5 degrees. Panels (G) and (H) show the surface morphology of the0.5iPDMS after only one iteration of the SIP strategy using1H,1H,2H,2H-perfluorodecyl methacrylate (FMA). Panel (I) shows a waterdroplet on the 0.5iPDMS surface after only one iteration of the SIPstrategy using FMA.

FIG. 3 shows a representative profiler scan of a 10⁻³iPDMS surface afterthe relayed surface-initiated polymerization (SIP) performed in FIG. 1using 1H,1H,2H,2H-perfluorodecyl methacrylate. The height of theresulting copolymers from the SIP strategy was up to 3 μm.

FIG. 4, panels (A)-(F), show representative scanning electron microscopeimages for samples after the relayed SIP. For all samples,oligo(ethylene glycol) methacrylate (OEGMA) and1H,1H,2H,2H-perfluorodecyl methacrylate (FMA) were used as the first andsecond monomer, respectively. Panels (A) and (B) show 0.5iPDMS after 1hour of the first SIP and 2 hours of the second SIP. The resultingcontact angle was 130 degrees. Panels (C) and (D) show 0.5iPDMS after 4hours of the first SIP and 2 hours of the second SIP. The resultingcontact angle was 130 degrees. Panels (E) and (F) show 10⁻³iPDMS after 2hours of the first SIP and 6 h of the second SIP. The resulting contactangle was 150 degrees.

FIG. 5, panels (A)-(D), show scanning electron microscope (SEM) imagesof the initiator integrated PDMS (iPDMS) surfaces after the relayedsurface-initiated polymerization (SIP). Panel (A) shows hydroxyethylmethacrylate (HEMA) as the second monomer for 0.5iPDMS. Panel (B) showsHEMA as the second monomer for 10⁻³iPDMS. Panel (C) shows methylmethacrylate (MMA) as the second monomer for 0.5iPDMS. Panel (D) showsOEGMA as the second monomer for 0.5iPDMS. The first monomer was OEGMA inall samples.

FIG. 6 shows the scanning electron microscope image of 10⁻⁶iPDMS afterrelayed SIP of 1H,1H,2H,2H-perfluorodecyl methacrylate (FMA). The numberof copolymers from the SIP strategy is much less than the 10⁻³iPDMS inFIG. 2, panel D.

DETAILED DESCRIPTION

Abbreviations and Definitions

Unless otherwise stated all temperatures are in degrees Celsius (° C.).Also, in these examples and elsewhere, abbreviations have the followingmeanings:

TABLE 1 Abbreviations Abbreviation Term A Amphere AscA Ascorbic Acid BEBinding Energy Bipy 2,2′-Bipyridine DMF Dimethylformamide Et3NtTriethylamine eV Electron Volts FMA 1H,1H,2H,2H-Perfluorodecylmethacrylate h Hour HEMA Hydroxyethyl methacrylate kV Kilovolt M MolarmA Milliamphere Mg Milligram Min Minutes mL Milliliter mM Millimolar mmMillimeter MMA Methyl Methacrylate mmol Millimole ms Millisecond nmNanometer μm Micrometer OEGMA Oligo(ethylene glycol) methyl methacrylatePa Pascal PDMS Poly(dimethyl siloxane) iPDMS Initiator Integrated PDMSPMDETA Pentamethyldiethylenetriamine s Second SE Standard Error SIPSurface-Induced Polymerization V Volt XPS X-ray PhotoelectronSpectroscopy

As used herein, certain terms may have the following defined meanings.

As used herein, the term “comprising” means that the compositions andmethods include the recited elements, but do not exclude others.“Consisting essentially of” when used to define compositions andmethods, shall mean excluding other elements of any essentialsignificance to the combination when used for the intended purpose.Thus, a composition consisting essentially of the elements as definedherein would not exclude trace contaminants or inert carriers.“Consisting of” shall mean excluding more than trace elements of otheringredients and substantial method steps for preparing the microfluidicdevice. Embodiments defined by each of these transition terms are withinthe scope of the present technology.

The term “hydrophobic surface” refers to a surface that is difficult towet. The term “superhydrophobic” surface refers to a hydrophobic surfacewhich has a contact angle of at least about 150 degrees. In someembodiments, the hydrophobic surface has a contact angle of at leastabout 155 degrees, or alternatively, at least about 160 degrees, oralternatively, at least about 165 degrees, or alternatively, at leastabout 170 degrees, or alternatively, at least about 175 degrees, oralternatively, about 180 degrees. The term “contact angle” refers to theangle at which a liquid interface meets a solid surface. On manyhydrophilic surfaces, water droplets will exhibit contact angles of 0degrees to 30 degrees. If the solid surface is hydrophobic, the contactangle will be larger than 90 degrees. On superhydrophobic surfaces thesurfaces have water contact angles as high as 150 degrees or even nearly180 degrees. On these surfaces, water droplets simply rest on thesurface, without actually wetting to any significant extent. Thesesurfaces are termed superhydrophobic.

The term “polymer substrate” refers to a solid polymer comprising atleast one base monomer and a linker to enable functionalization of thepolymer substrate surface. The size of the polymer substrate is easilydetermined by one of skill in the art. It is contemplated that the sizeof the polymer substrate is not limited by any of the physicalcharacteristics of the polymer. In addition, the shape of the polymersubstrate can be dictated by the use of a mold. Such molds are wellknown to those of skill in the art. In some instances, at least two basemonomers are used to make the polymer substrate. In some cases, basemonomers comprise a polydimethylsiloxane having at least one vinyl groupand a silicon hydride containing monomer, such that the silicon hydridecontaining monomer forms more than one covalent bond with at least onevinyl group on the polydimethylsiloxane and the resulting polymersubstrate has a density of about 1 g mL⁻¹ and a contact angle of about100 degrees to about 115 degrees. In some embodiments, thepolydimethylsiloxane comprises a sufficient number of vinyl groups suchthat the physical properties of the resulting polymer substrate can beused to make the superhydrophobic surface. In addition, the siliconhydride containing monomer comprises a sufficient number of Si—H groupssuch that the physical properties of the resulting polymer substrate canbe used to make the superhydrophobic surface. The base monomer mixturesmay comprise additional components, such as other monomers or acatalyst, such as platinum. Various monomer mixtures are commerciallyavailable and include, for example, Sylgard® 184 (Dow CorningCorporation, Midland, Mich., United States), RTV 615 (Sil-Mid limited,Coleshill, West Midlands, United Kingdom) and ELASTOSiL® RT 601 (WackerChemie AG, San Jose, Calif., United States).

The polymer substrate further comprises a linker to enablefunctionalization of the polymer substrate surface wherein the firstlinker is incorporated into the polymer substrate at a substantially lowconcentration. In some embodiments, the linker is incorporated thereinat a sufficient concentration to provide a surface density of about3×10⁻⁴ to about 9×10⁻⁸. In some embodiments, the linker is incorporatedtherein at a sufficient concentration to provide a surface density ofabout 1×10⁻⁵. In some embodiments, the volume to volume base monomer tolinker ratio is about 11:10⁻³.

The term “linker” refers to a chain of atoms having from 1 to 40 atoms.Each linker may be linear, branched or cyclic and may be homogenous orheterogeneous in its atom content (e.g., linkers containing only carbonatoms or linkers containing carbon atoms as well as one or moreheteroatoms present on the linker in the form of a hydroxyl, ketone,aldehyde, carboxyl, amine, amide, carbamate, urea, thiol, ether, etc.,or residues thereof). In some embodiments, the linker contains 1 to 25carbon atoms and 0 to 15 heteroatoms.

The term “bonded” refers to a chemical bond. Various types of chemicalbonds can be employed in the methods disclosed herein, either alone orin combination. Examples of bonds include a covalent bond, a polarcovalent bond, an ionic bond and a hydrogen bond.

The term “monomer” has the meaning understood by those skilled in thechemical art. That is, a monomer is a chemical compound that is capableof forming a macromolecule of repeating units of itself, i.e., apolymer. The term “monomer” is also intended to include “oligomers”which consists of more than one monomer unit. In some embodiments, themonomer is a hydrophobic monomer.

The terms “hydrophobic monomer” and “substantially hydrophobic monomer”refer to a monomer that, once polymerized, is sufficiently hydrophobicto form the superhydrophobic coating disclosed herein. In someembodiments, the hydrophobic monomer comprises fluorine. In someembodiments, the hydrophobic monomer comprises at least 10 fluorineatoms. Examples of hydrophobic monomers that can be used in the methodsdisclosed herein, are 1H,1H,2H,2H-perfluorodecyl methacrylate,2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate,4,4,5,5,6,6,7,7,8,9,9,9-dodecafluoro-2-hydroxy-8-(trifluoromethyl)nonylmethacrylate,3,3,4,4,5,5,6,6,7,8,8,8-dodecafluoro-7-(trifluoromethyl)octyl acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,12,12,12-eicosafluoro-11-(trifluoromethyl)dodecylmethacrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluorododecylacrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluorododecylmethacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecylmethacrylate,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoro-2-hydroxyundecylacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,10,10,10-hexadecafluoro-9-(trifluoromethyl)decylacrylate,3,3,4,4,5,5,6,6,7,7,8,8,9,10,10,10-hexadecafluoro-9-(trifluoromethyl)decylmethacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate,1,1,1,3,3,3-hexafluoroisopropyl acrylate,4,4,5,5,6,7,7,7-octafluoro-2-hydroxy-6-(trifluoromethyl)heptyl acrylate,4,4,5,5,6,7,7,7-octafluoro-2-hydroxy-6-(trifluoromethyl)heptylmethacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl acrylate,2,2,3,3,4,4,5,5-octafluoropentyl methacrylate,3,3,4,4,5,6,6,6-octafluoro-5-(trifluoromethyl)hexyl methacrylate,2,2,3,3,3-pentafluoropropyl acrylate,4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-2-hydroxynonyl acrylate,3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl acrylate,2,2,2-trifluoroethyl acrylate, Zonyl® TM fluoromonomer (Sigma Aldrich),[2,2,3,3,4,5,5,5-octafluoro-4-(trifluoromethyl)pentyl]oxirane,(2,2,3,3,4,4,5,5,5-nonafluoropentyl)oxirane,[2,2,3,3,4,4,5,5,6,6,7,7,8,9,9,9-hexadecafluoro-8-(trifluoromethyl)nonyl]oxirane,(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononyl)oxirane,glycidyl 2,2,3,3,4,4,5,5-octafluoropentyl ether, glycidyl2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl ether, and the like. In oneembodiment, the hydrophobic monomer is 1H,1H,2H,2H-perfluorodecylmethacrylate.

The term “polymer layer” refers to a polymer that is in contact with andlayered on the surface of a polymer substrate. The SIP strategydisclosed herein yields a superhydrophobic coating having more than onepolymer in contact with the surface of the polymer substrate. Herein, afirst polymer layer is in contact with a first linker and a secondpolymer layer in contact with a second linker. It is contemplated thatthe height of the polymer layers can vary, provided that the combinedheight of all layers deposited in the SIP strategy result in a totalheight of greater than about 1000 nm and a width of greater than about200 nm.

The term “polyether” refers to compounds which contain more than oneether group. Various polyethers can be utilized in the disclosedmethods, such as for example polyethylene glycol and polypropyleneglycol. In some embodiments, the polyether also comprises apolymerizable group. Various polymerizable groups can be used in themethods disclosed herein, such as an acrylate, methacrylate, vinylketone, methylvinyl ketone, acrylamide and methacrylamide. In someembodiments, the polyether has a molecular weight of about 100 to about1000 g/mol. Alternatively, the polyether has a molecular weight of about200 to about 900 g/mol, or alternatively, about 300 to about 800 g/mol,or alternatively, about 400 to about 700 g/mol, or alternatively, about500 to about 600 g/mol. The polyethers can also be branched or linear.In some embodiments, the monomer is oligo(ethylene glycol) methacrylate.

The term “prepolymer” refers to a reactive low-molecular-weightmacromolecule or an oligomer, capable of further polymerization.Examples of prepolymers include, but are not limited to, e.g.,poly(dimethyl-methylvinylsiloxane) prepolymer andpoly(dimethyl-methylhydrogensiloxane) precursors. The term“poly(dimethylmethylhydrogensiloxane) precursors” refers to a reactivelow-molecular-weight macromolecule or an oligomer ofdimethylmethylhydrogensiloxane, capable of further polymerization.Polymerization of these prepolymers or monomers can be accomplished by,as an example, free radical polymerization, metal catalyzedpolymerization, heat, or combination thereof. In some embodiments,polymerization is accomplished using both metal catalyzed polymerizationand heat.

The term “reaction conditions” refers to conditions which comprisesolvent (if required), time, temperature, pressure, concentration, andthe like. It is well known to those skilled in the art that the reactionconditions may vary depending on the components which are being reacted.

The term “substantially low concentration” refers to the concentrationof linker required to yield a superhydrophobic surface. Although it isdifficult to discern the exact density of the first linker on theinitiator integrated PDMS (iPDMS) surface, one could reasonably assumethat the amount of initiator integrated into the network of iPDMS isproportional to the feed ratio of the starting components. The feedratio of the starting components can vary depending on the compositionof the base monomers used. In some embodiments, the first linker isincorporated into the polymer substrate at a volume to volume ratio ofabout 11:10⁻³. In embodiments wherein more than one base monomer isused, the ratio of first and second base monomer to first initiator isabout 10:1:10⁻³. In some embodiments, the polymer substrate has a firstlinker incorporated therein at a concentration to provide a surfacedensity of from about 3×10⁻⁴ to about 9×10⁻⁸ units per nm².Alternatively, the polymer substrate has a first linker incorporatedtherein at a concentration to provide a surface density of from about4×10⁻⁴ to about 5×10⁻⁷ units per nm², or alternatively, from about5×10⁻⁴ to about 1×10⁻⁷, or alternatively, from about 6×10⁻⁴ to about5×10⁻⁶, or alternatively, from about 7×10⁻⁴ to about 1×10⁻⁶, oralternatively, from about 8×10⁻⁴ to about 5×10⁻⁵ or alternatively, fromabout 9×10⁻⁴ to about 2×10⁻⁵ units per nm², or alternatively, about1.0×10⁻⁵ units per nm².

The term “alkyl” refers to saturated monovalent hydrocarbyl groupshaving from 1 to 25 carbon atoms, more particularly from 6 to 12 carbonatoms. The alkyl group can be branched or linear. This term isexemplified by groups such as methyl, ethyl, n-propyl, iso-propyl,n-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl,n-decyl, n-dodecyl, and the like.

The term “functional group” refers to atoms or small groups of atoms(e.g., two to five) that exhibit a characteristic reactivity whentreated with certain reagents. This term is exemplified by groups suchas alkyl halides, a terminal alkene or alkyne, alcohols, thiols,sulfides, amines, and carbonyl derivatives, such as aldehydes, ketones,esters and alpha-haloesters.

The term “alkyl halide” refers to a chemical compound, consisting of analkyl group as defined herein, wherein a hydrogen is replaced by atleast one halogen atom.

The term “halide”, “halo” or “halogen” refers to fluorine, chlorine,bromine and iodine.

The term “terminal alkene” refers to a functional group of the formula—CH═CH₂, which is bound to a carbon atom of an alkyl group.

The term “terminal alkyne” refers to refers to a functional group of theformula —C≡CH, which is bound to a carbon atom of an alkyl group.

The term “hydroxyl” refers to —OH. The term “alcohol” refers to ahydroxyl moiety which is bound to a carbon atom.

The term “thiol” refers to —SH.

The term “sulfide” refers to —S—S—.

The term “amine” refers to —NH₂.

The term “carbonyl derivatives” refers to functional groups composed ofa carbon atom double-bonded to an oxygen atom: C═O. Examples of carbonylderivatives include, but are not limited to, aldehydes, ketones,carboxylic acids, esters, amides, acyl halides, acid anhydrides, ureas,carbamates, and the like.

The term “aldehyde” refers to a functional group composed of a carbonatom bonded to a hydrogen atom and double-bonded to an oxygen atomyielding a terminal carbonyl group: —CH═O.

The term “ketone” refers to a functional group characterized by acarbonyl group (O═C<) bonded to two other carbon atoms.

The term “ester” refers to a functional group composed of a carbon atombonded to an oxygen atom, a carbon atom and double-bonded to an oxygenatom. Esters, as used herein can have the chemical formula —(C═O)—O— or—O—(C═O)—.

The term “carboxyl” refers to —COOH.

The term “amide” refers to —NR—(C═O)—, where R can be hydrogen or alkyl.

The term “carbamate” refers to the functional group —NR(CO)O—, where Rcan be hydrogen or alkyl.

The term “urea” refers to a functional group —NR(CO)NR—, where R can behydrogen or alkyl.

The term “ether” refers to a functional group having an oxygen atombonded to two carbon atoms (—C—O—C—).

The term “alpha-haloester” refers to a functional group comprising anester and an alkyl halide, wherein the alkyl halide is bonded to thecarbonyl carbon of the ester moiety. In some embodiments, analpha-haloester as disclosed herein is of the formula X—CR₂—CO—O— or—O—(C═O)—CR₂—X, wherein each R is independently hydrogen or alkyl, and Xis a halogen. In some embodiments, the halogen is bromine.

The term “acrylate” refers to CH₂═CHCOO—.

The term “methacrylate” refers to CH₂═C(CH₃)COO—.

The term “vinyl ketone” refers to CH₂═CHCO—.

The term “methylvinyl ketone” refers to CH₂═C(CH₃)CO—.

The term “acrylamide” refers to CH₂═CHCONR—, where R is hydrogen oralkyl.

The term “methacrylamide” refers to CH₂═C(CH₃)CONR—, where R is hydrogenor alkyl.

The term “acyl halide” refers to a functional group comprising acarbonyl group singly bonded to a halogen atom. Examples of acyl halidesinclude —(C═O)Cl and —(C═O)Br.

The term “protein resistant” refers to a surface that does notsignificantly contact a protein. In addition, for many assayapplications, it would be desirable that the surface does not impede themovement of proteins. Many coatings are not amenable for use withproteins as they are known to stick to or be attracted to many of theknown surface coatings. For many applications, such as assays,lab-on-chips, and the like, it is desirable that the surface besufficiently protein resistant as not to adversely effect the experimentoutcome.

Hydrophobic Coatings

Superhydrophobic PDMS surfaces have attracted much research effort andhave been produced by methods such as replicating from an artificial(He, B., et al., Langmuir 2003, 19, 4999-5003) or a natural mold (i.e.,the lotus leaf, Sun, M. H., et al., Langmuir 2005, 21, 8978-8981), laseretching (Jin, M. H., et al., Macromol. Rapid Commun. 2005, 26,1805-1809), and mechanical assisted self-assembled monolayer (Genzer,J., et al., Science 2000, 290, 2130-2133). However, these methods cannotbe applied to modifying the wall of pre-formed microfluidic channels.Furthermore, known methods for the functionalization of PDMS relies onthe ability to first fabricate a functionalized PDMS.

Surface-initiated polymerization (SIP) has been conducted on substratesof high initiator concentration for the purpose of generating polymerbrushes of extremely high density. Although the high density of polymerchains led to many unique properties (Tsujii, Y.; Ohno, K.; Yamamoto,S.; Goto, A.; Fukuda, T., Structure and properties of high densitypolymer brushes prepared by surface-initiated living radicalpolymerization. In Surface-Initiated Polymerization I, 2006; Vol. 197,pp 1-45), the increase of polymer chain density did not lead tosuperhydrophobicity. SIP, however, is advantageous not only for itsability to create high density polymer brushes but also for that SIPprovided better structural control of the resulting coatings.

The superhydrophobic coatings disclosed herein are the result of arelayed SIP strategy which includes the deposition of more than onepolymer layer onto the surface of a polymer substrate. In addition,three factors are optimized in the coating described herein to achievethe superhydrophobic surfaces. These factors include: 1) an ultra lowinitiator density, 2) the relayed SIP strategy, and 3) a hydrophobicmonomer.

Disclosed herein is a hydrophobic coating having a contact angle of atleast about 150 degrees, which coating comprises:

-   -   a polymer substrate comprising a first linker incorporated        therein at a specified surface density of from about 3×10⁻⁴ to        about 9×10⁻⁸ units per nm²;    -   a first polymer layer in contact with said first linker;    -   a second linker in contact with said first polymer layer; and    -   a second polymer layer in contact with said second linker.

The polymer substrate is a solid polymer comprising at least one basemonomer and a linker to enable functionalization of the polymersubstrate surface. The size of the polymer substrate is easilydetermined by one of skill in the art. It is contemplated that the sizeof the polymer substrate is not limited by any of the physicalcharacteristics of the polymer. In addition, the shape of the polymersubstrate can be dictated by the use of a mold. Such molds are wellknown to those of skill in the art. In some embodiments, the polymersubstrate comprises poly(dimethyl) siloxane (PDMS). In some instances,at least two base monomers are used to make the polymer substrate.Various monomer mixtures can be used in addition with the first linkerto form the polymer substrate. Examples of these include, but are notlimited to, Sylgard® 184 (Dow Corning Corporation Midland, UnitedStates), RTV 615 (Sil-Mid limited, Coleshill, West Midlands, UnitedKingdom), and ELASTOSiL® RT 601 (Wacker Chemie AG, San Jose, Calif.,United States).

The polymer substrate further comprises a linker to enablefunctionalization of the polymer substrate surface, wherein the firstlinker is incorporated therein at a specified surface density of fromabout 3×10⁻⁴ to about 9×10⁻⁸ units per nm². In some embodiments, thefirst linker is incorporated at a surface density of about 1.0×10⁻⁵units per nm². The surface density of the first linker is calculatedbased on the assumption that the first linker is evenly distributedthroughout the PDMS network. In some embodiments, the first linker isincorporated into the polymer substrate at a volume to volume ratio ofabout 11:10⁻³. In embodiments wherein more than one base monomer isused, the ratio of first and second base monomer to the first initiatoris about 10:1:10⁻³. In some embodiments, the first linker comprises analkyl group with a terminal functional group. In some embodiments, thefirst linker comprises a linear (C₆-C₁₂) alkyl group with a terminalalpha-haloester group.

The SIP strategy disclosed herein yields a superhydrophobic coatinghaving more than one polymer in contact with the surface of the polymersubstrate. Herein, the first polymer layer is in contact with the firstlinker. In some embodiments, the first polymer layer is bonded to thefirst linker. In some embodiments, the first polymer layer is bonded tothe first linker by a carbon-carbon bond. The height of each of thepolymer layers is largely dependent on the polymerization reaction time.It is contemplated that the height of the polymer layers can vary,provided that the combined height of all layers deposited in the SIPstrategy result in a total height of greater than about 1000 nm and awidth of the polymer nodes of greater than about 200 nm. In someembodiments, the height of the first polymer layer is about 2 μm to 5μm. In some embodiments, the height of the first polymer layer is about3 μm. It is further contemplated that the width of the first polymerlayer should be between about 100 nm to about 500 nm (see FIG. 2, panels(G) and (I)). Alternatively, the width can be from about 200 nm to about400 nm, or alternatively, about 200 nm to about 300 nm. In someembodiments, the width of the polymer layer is about 300 nm.

In some embodiments, the first polymer layer comprises a polyether.Various polyethers can be utilized in the disclosed methods, such as forexample polyethylene glycol and polypropylene glycol. In someembodiments, the polyether also comprises a polymerizable group. Variouspolymerizable groups can be used in the methods disclosed herein, suchas an acrylate, methacrylate, vinyl ketone, methylvinyl ketone,acrylamide and methacrylamide. In some embodiments, the polyether has amolecular weight of about 100 to about 1000 g/mol. Alternatively, thepolyether has a molecular weight of about 200 to about 900 g/mol, oralternatively, about 300 to about 800 g/mol, or alternatively, about 400to about 700 g/mol, or alternatively, about 500 to about 600 g/mol. Thepolyethers can also be branched or linear. In some embodiments, thefirst polymer layer comprises polyethylene glycol. In some embodiments,the monomer is oligo(ethylene glycol) methacrylate.

The superhydrophobic coating disclosed herein comprises a second polymerlayer in contact with the first polymer layer. In some embodiments, thefirst and second polymer layers contact each other via a second linkerwhich is in contact with the first and second polymer layers. In someembodiments, the second linker is bonded to the first polymer layer. Insome embodiments, the bond is an ester bond. In some embodiments, thesecond linker comprises a carbonyl group.

In some embodiments, the second linker is bonded to the first and secondpolymer layer. In some embodiments, the bond is a carbon-carbon bond.

As stated herein, one factor required to achieve the superhydrophobicsurfaces is a substantially hydrophobic monomer. Thus, the outermostpolymer layer on the superhydrophobic surface comprises a substantiallyhydrophobic monomer. In some embodiments, the second polymer layer isthe outermost layer on an article. The height second polymer layer ofeach of the polymer layers is largely dependent on the polymerizationreaction time. It is contemplated that the height of the polymer layerscan vary, provided that the combined height of all layers deposited inthe SIP strategy result in a total height of greater than about 1000 nmand a width of greater than about 200 nm. In some embodiments, thesecond polymer layer comprises fluorine.

Also disclosed herein is a hydrophobic coating having a contact angle ofat least about 150°, which coating comprises:

-   -   a poly(dimethyl) siloxane substrate comprising a first linker        incorporated therein at a surface density of from about 3×10⁻⁴        to about 9×10⁻⁸ units per nm²;    -   a polyether layer in contact with said first linker;    -   a second linker in contact with to said polyether layer; and    -   a fluorinated polymer layer in contact with said second linker.        Methods for Making a Hydrophobic Coating Using a Relayed        Surface-Initiated Polymerization (SIP) Strategy

The relayed surface-initiated polymerization (SIP) strategy involvesthree factors which are optimized in the coating described herein toachieve the superhydrophobic surfaces. These factors include: 1) anultra low initiator density, 2) the relayed SIP strategy, and 3) ahydrophobic monomer.

Disclosed herein is a method of making a hydrophobic coating having acontact angle of at least about 150 degrees, said method comprising:

-   -   1) providing a polymer substrate wherein a first linker is        incorporated into the substrate at a surface density of from        about 3×10⁻⁴ to about 9×10⁻⁸ units per nm²;    -   2) contacting a monomer with said first linker under first        polymerizing conditions to provide a first polymer layer bound        to the polymer substrate through the first linker;    -   3) contacting a second linker with said first polymer layer        under reaction conditions to provide a reactive surface; and    -   4) contacting a monomer with said reactive surface under second        polymerizing conditions to provide the hydrophobic coating.

The relayed surface-initiated polymerization (SIP) strategy begins byproviding a polymer substrate wherein a first linker is incorporatedinto the substrate at a surface density of from about 3×10⁻⁴ to about9×10⁻⁸ units per nm². The polymer substrate is provided by polymerizinga monomer mixture comprising at least one base monomer and asubstantially low concentration of a first linker. In some embodiments,the method further comprises a second base monomer.

Various base monomers can be employed to make the polymer substrate. Insome embodiments, at least two base monomers are used to make thepolymer substrate. In some embodiments, base monomers comprise apolydimethylsiloxane having at least one vinyl group and a siliconhydride containing monomer, wherein the silicon hydride forms a covalentbond with the vinyl groups. In some cases, base monomers comprise apolydimethylsiloxane having at least one vinyl group and a siliconhydride containing monomer, such that the silicon hydride containingmonomer forms more than one covalent bond with at least one vinyl groupon the polydimethylsiloxane and the resulting polymer substrate has adensity of about 1 g mL⁻¹ and a contact angle of about 100 degrees toabout 115 degrees. In some embodiments, the at least one base monomer isa poly(dimethyl-methylvinylsiloxane) prepolymer. In some embodiments,the second base monomer comprises apoly(dimethyl-methylhydrogensiloxane) precursor.

The base monomer mixtures may comprise additional components, such asother monomers or a catalyst, such as platinum. Various monomer mixturesare commercially available and include, for example, Sylgard® 184 (DowCorning Corporation Midland, Mich., United States), RTV 615 (Sil-Midlimited, Coleshill, West Midlands, United Kingdom), and ELASTOSiL® RT601 (Wacker Chemie AG, San Jose, Calif., United States).

The polymer substrate further comprises a linker to enablefunctionalization of the polymer substrate surface. In some embodiments,the surface density of the linker is about 1.0×10⁻⁵ units per nm². Thesurface density of the first linker is calculated based on theassumption that the first linker is evenly distributed throughout thePDMS network. In some embodiments, the polymer substrate has the firstlinker incorporated therein at a volume to volume ratio of about11:10⁻³. Alternatively, in some embodiments, the first linkerincorporated therein at a volume to volume ratio of from about 11:5×10⁻²to about 11:5×10⁻⁵, or alternatively, from about 11:5×10⁻² to about11:10⁻⁵, or alternatively, from about 11:5×10⁻² to about 11:5×10⁻⁴, oralternatively, from about 11:5×10⁻² to about 11:10, or alternatively,from about 11:5×10⁻² to about 11:10⁻⁴. In embodiments wherein more thanone base monomer is used. In some embodiments, the volume to volumeratio of first and second base monomer to first linker is about10:1:10⁻³.

In some embodiments, the first linker comprises an alkyl group furthercomprising at least one terminal unreacted functional group. Variousfunctional groups can be employed in the methods disclosed herein.Examples of functional groups include, but is not limited to, e.g.,alkyl halides, a terminal alkene or alkyne, alcohols, thiols, sulfides,amines, and carbonyl derivatives, such as aldehydes, ketones and esters.In some embodiments, the at least one terminal unreacted functionalgroup is an alpha-haloester. In some embodiments, the first linker isundec-10-enyl-2-bromo-2-methylpropanoate which has the structure shownbelow.

The polymerization of the at least one base monomer and first linkerprovides the polymer substrate. In some cases the polymer substrate iscured at about 80° C. for about 2 hours. Higher temperatures such asthis can be used to decrease the polymerization or curing time althoughthe polymer substrate can be polymerized at room temperature (about 25°C.) for about one day. As would be obvious to one of skill in the art,the exact polymerization conditions used can vary greatly based on therequirements for a given monomer mixture.

After polymerization of the polymer substrate, a first polymer layer isdeposited onto the surface. This is referred to as the first SIP and canbe accomplished by contacting a monomer with the first linker underfirst polymerizing conditions to provide a first polymer layer bound tothe polymer substrate through the first linker. In some embodiments, thereaction conditions comprise first forming a monomer mixture comprisinga catalyst prior to contacting the polymer substrate. In someembodiments, the first polymerizing conditions comprise heating themonomer and linker to a temperature of from about 30° C. to about 90° C.Alternatively, in some embodiments, the first polymerizing conditionscomprise allowing the monomer react with the polymer substrate for about2 hours at room temperature (about 25° C.). In some embodiments, thefirst polymerizing conditions comprise a deoxygenating step.

The height of each of the polymer layers is largely dependent on thepolymerization reaction time. It is contemplated that the height of thepolymer layers can vary, provided that the combined height of all layersdeposited in the SIP strategy result in a total height of greater thanabout 1000 nm and a width of greater than about 200 nm. In someembodiments, the height of the first polymer layer is about 2 μm to 5μm. In some embodiments, the height of the first polymer layer is about3 μm. It is further contemplated that the width of the first polymerlayer should be between about 100 nm to about 500 nm (see FIG. 2, panels(G) and (I)). Alternatively, the width can be from about 200 nm to about400 nm, or alternatively, about 200 nm to 300 nm. In some embodiments,the width of the polymer layer is about 300 nm.

In some embodiments, the monomer comprises at least one functional groupselected from the group consisting of an alkyl halide, a terminal alkeneor alkyne, hydroxyl, thiol, sulfide, amine, and carbonyl derivative,such as aldehyde, ketone, ester and alpha-haloester. In someembodiments, the monomer comprises at least one hydroxyl group. In someembodiments the monomer comprises a polyether. “Polyether” compoundscontain more than one ether group. Various polyethers can be utilized inthe disclosed methods, such as, for example, polyethylene glycol andpolypropylene glycol. In some embodiments, the polyether also comprisesa polymerizable group. Various polymerizable groups can be used in themethods disclosed herein, such as an acrylate, methacrylate, vinylketone, methylvinyl ketone, acrylamide and methacrylamide. Thepolyethers can also be branched or linear. In some embodiments, themonomer is oligo(ethylene glycol) methacrylate.

The next step of the SIP strategy involves contacting a second linkerwith said first polymer layer under reaction conditions to provide areactive surface. A reactive surface is needed in order to successfullydeposit the second polymer layer. This can be accomplished by the use ofa second linker. In some embodiments, the second linker comprises atleast two reactive functional groups. Various reactive functional groupscan be employed, such as acyl halides, esters, alkyl halides, amides,and the like. In some embodiments, the second linker comprises an acylhalide. In some embodiments, the second linker is 2-bromoisobutyrylbromide.

In some embodiments, the reaction conditions comprise acetylationconditions which are well known in the art. In general, the reactionconditions depend on the functional groups of the second linker. Thesereaction conditions would be apparent to one of skill in the art. Forexample, when the second linker comprises an acyl halide, the reactionconditions comprise acetylation conditions. These acetylation conditionsmight comprise cooling the intermediate polymer substrate to about 0°C., followed by the addition of a base, such as a tertiary amine, andaddition of the second linker dropwise. Other reactions conditions, suchas the solvent and time may vary depending on the nature of the secondlinker. In some embodiments, the reaction time is about 30 to 45minutes.

Once the reactive surface is formed, the second polymer layer can bedeposited. This is referred to as the first SIP and can be accomplishedby contacting a monomer with said reactive surface under secondpolymerizing conditions thus providing the hydrophobic coating. Asdiscussed herein, one of the factors required to achieve thesuperhydrophobic surface is the incorporation of a substantiallyhydrophobic monomer as the outermost polymer layer. In some embodiments,the second polymer layer is the outermost layer. Various hydrophobicmonomers can be used in the methods disclosed herein and are known tothose of skill in the art. In some embodiments, the second polymer layercomprises fluorine. In some embodiments, the substantially hydrophobicmonomer is 1H,1H,2H,2H-perfluorodecyl methacrylate.

In some embodiments, the second polymerizing conditions comprise heatingthe monomers to about 80° C. In some embodiments, the reactionconditions comprise first forming a monomer mixture comprising acatalyst prior to contacting the second linker. In some embodiments, thesecond polymerizing conditions comprise heating the monomer and linkerto a temperature of from about 25° C. to about 90° C. Alternatively, insome embodiments, the second polymerizing conditions comprise allowingthe monomer to react with the polymer substrate for about 2 hours atroom temperature (about 25° C.). Again, the height of each of thepolymer layers is largely dependent on the polymerization reaction time.It is contemplated that the height of the polymer layers can vary,provided that the combined height of all layers deposited in the SIPstrategy result in a total height of greater than about 1000 nm and awidth of greater than about 200 nm. In some embodiments, the secondpolymerizing conditions comprise a deoxygenating step.

Also disclosed herein is a method for making a hydrophobic coatinghaving a contact angle of at least about 150 degrees, said methodcomprising:

-   -   1) polymerizing a mixture comprising a        poly(dimethyl-methylvinylsiloxane) prepolymer,        poly(dimethyl-methylhydrogensiloxane) precursors and        undec-10-enyl-2-bromo-2-methylpropanoate, under thermal        conditions to form a polymer substrate;    -   2) contacting oligo(ethylene glycol) methacrylate with said        polymer substrate under first polymerizing conditions to provide        a first polymer layer bound to the polymer substrate through the        undec-10-enyl-2-bromo-2-methylpropanoate;    -   3) contacting 2-bromoisobutyryl bromide with said first polymer        layer under reaction conditions to provide a reactive surface;        and    -   4) contacting 1H,1H,2H,2H-perfluorodecyl methacrylate with said        reactive surface under second polymerizing conditions to provide        the hydrophobic coating.

In some embodiments, the polymerization conditions can result in variouspolymerization mechanisms. Various types of polymerizations can be usedsuch as, for example, cationic, anionic, free radical and livingpolymerizations. Such polymerizations can be metal catalyzedpolymerization reactions. In some embodiments, the polymerizationconditions comprise a metal catalyst. Various metals can be used as acatalyst herein, such as, platinum, copper, iron, manganese, cobalt,molybdenum, tin, zinc, ruthenium, rhodium, and the like. In someembodiments, the metal comprises copper. In some embodiments, the firstpolymerizing conditions comprises metal catalyzed polymerization. Insome embodiments, the second polymerizing conditions comprises metalcatalyzed polymerization.

Uses for the Superhydrophobic Coating(s)

Disclosed herein is a simple surface initiated polymerization (SIP)method to render a surface superhydrophobic. Three factors are allrequired to achieve the superhydrophobic surfaces, namely, the ultra lowinitiator density, the relayed SIP strategy, and the hydrophobicmonomer.

In some embodiments, the superhydrophobic surface is used to produce amicrofluidic device, comprising at least one channel disposed thereon.Since microfluidic technology is based on the manipulation of liquidflow through microfabricated channels, the ability to control the liquidflow is desired. In some embodiments, the microfluidic device comprisesthe hydrophobic coating disclosed herein on at least a portion of thesurface.

In addition, the in situ modification of an internal wall of amicrofluidic channel made from iPDMS can be performed and used asmicrofluidic devices. In some embodiments, the hydrophobic coatingdisclosed herein is on at least a portion of the walls of themicrofluidic channels.

Microfluidic devices comprising the hydrophobic surface disclosed hereinwould be useful in the area of biotechnology, e.g., the “lab-on-a-chip”.Current “lab-on-a-chip” devices are non-ideal due to the fact thatphysical and chemical effects become more dominant on a small-scale, andeffects such as capillary forces, surface roughness and chemicalinteractions of construction materials on reaction processes can beenhanced.

In some embodiments, the hydrophobic coating disclosed herein is proteinresistant (Gudipati, C. S., et al., Langmuir 2005, 21, 3044-3053). Thus,in some embodiments, the hydrophobic coating is used to provide articleswhich are protein resistant. This enables the production of variousprotein resistant articles, such as microfluidic devices, which can beused for analytical and/or purification assays, and the like. Thesuperhydrophobi coating disclosed herein inhibited protein(fluorescently labeled bovine serum albumin) adsorption and smallmolecule (Rhodamine B) absorption to the level undetectable byfluorescent microscope, which were long standing problems inmicrofluidics (Huang, B., et al., Science 2007, 315, 81-84, Roman, G.T., et al., Anal. Chem. 2005, 77, 1414-1422, Toepke, M. W., et al., LabChip 2006, 6, 1484-1486, Song, H., et al., Anal. Chem. 2006, 78,4839-4849).

In addition to microfluidic devices and “lab-on-chips”, the hydrophobiccoating disclosed herein can be used anywhere that a hydrophobic coatingis desired. For example, many objects, such as boats and marinemonitoring devices, which are continually exposed to the ocean require aprotective coating to preserve their utility. Therefore, these methodscan also be applied to provide marine anti-fouling materials (Genzer,J., et al., Biofouling 2006, 22, 339-360). In some embodiments, thehydrophobic coating is used to produce articles which are marineantifoulable.

In some embodiments, the hydrophobic coating is used to produce articleswhich provides a surfaces for sliding behavior study for purposes ofmaterials engineering (Granick, S., et al., Nat. Mater. 2003, 2,221-227).

EXAMPLES

All numerical designations, e.g., pH, temperature, time, concentration,and molecular weight, including ranges, are approximations which arevaried (+) or (−) by increments of 0.1. It is to be understood, althoughnot always explicitly stated that all numerical designations arepreceded by the term “about”. It also is to be understood, although notalways explicitly stated, that the reagents described herein are merelyexemplary and that equivalents of such are known in the art.

These and other embodiments of the present technology will readily occurto those of ordinary skill in the art in view of the disclosure hereinand are specifically contemplated.

The present technology is further understood by reference to thefollowing examples, which are intended to be purely exemplary of thepresent technology. The present technology is not limited in scope bythe exemplified embodiments, which are intended as illustrations ofsingle aspects of the present technology only. Any methods that arefunctionally equivalent are within the scope of the present technology.Various modifications of the present technology in addition to thosedescribed herein will become apparent to those skilled in the art fromthe foregoing description and accompanying figures. Such modificationsfall within the scope of the appended claims.

The vinyl terminated initiator (v-initiator, undec-10-enyl2-bromo-2-methylpropanoate) was obtained from HZDW (99%, Hangzhou,China). Oligo(ethylene glycol) methyl methacrylate (OEGMA, 98%),1H,1H,2H,2H-perfluorodecyl methacrylate (FMA, 99%), methyl methacrylate(MMA, 99%), hydroxyethyl methacrylate (HEMA, 97%), and 2-bromoisobutyrylbromide (98%) were purchased from Aldrich and used as received. AHITACH-54800 scanning electron microscope was used to characterize iPDMSsurfaces. The microscope was operated at 10.0 kV. Prior to measurements,the samples were coated with a thin gold film by means of a vacuumsputter to improve electrical conductivity. Water contact angles weremeasured on a Dataphysics OCA20 contact angle system at roomtemperature. All data was collected and analyzed using software providedby the manufacturer.

Example 1 SIP from iPDMS

Sylgard 184 was used as a model PDMS elastomer, which was commerciallyavailable from Dow Corning and consisted of liquid components A (amixture of catalyst Pt and prepolymer dimethylsiloxane with vinylgroups) and B (prepolymer dimethylsiloxane with vinyl groups and Si—Hgroups). PDMS and initiator integrated PDMS (iPDMS) substrates (flatsurface and as the walls of microfluidic channels) were prepared bythoroughly mixing the three components A, B (from Sylgard 184) and C(initiator) at a desired volume/volume ratio (A:B:C=10:1:C, C variedfrom 0.5 to 10⁻⁶) and cured at 80° C. for 2 h.

For the SIP of OEGMA, the reaction mixture was prepared by thoroughlymixing two parts. Part 1 was a transparent, pale-blue solution, preparedby adding a specified amount of CuCl₂ (5.4 mg, 0.4 mmol),2,2′-bipyridine (Bipy, 12.5 mg, 0.8 mmol, i.e., 1:2 mole ratio) and afixed amount monomer to 5 mL Milli-Q water. Part 2 was a colorlesssolution, prepared by adding a specified amount of ascorbic acid (AscA,7.0 mg, 0.4 mmol) to 5 mL Milli-Q water. Both solutions weredeoxygenated and the two parts were mixed together under a nitrogenatmosphere. The mixture was further deoxygenated and the resultingmixture was red in color due to the reduction of deactivator Cu(II)/Bipycomplex to activator Cu(I)/Bipy complex. The resulting mixture had amole ratio of monomer/CuC12/Bipy/AscA=200/1/2/1, with a feed CuC1₂concentration of 0.04 mM. This mixture was then transferred to areaction setup under nitrogen atmosphere and SIP was initiated andcontinued for 120 min at about 25° C. The polymerization was stoppedwhen iPDMS was removed from the solution. Samples were thoroughly rinsedwith methanol, Milli-Q water, and dried under flowing nitrogen beforefurther treatment.

After the first SIP, the iPDMS was functionalized with bromoisobutyrylbromide as the initiation moiety. Samples were immersed inN,N-Dimethylformamide (DMF) (70 mL) at 0° C., and Et₃N (1.16 mL, 7 mmol)was added dropwise, the concentration of Et₃N in DMF was kept at 0.1 M.After the mixture was stirred for about 10 min, we then added dropwiseBrCOC(CH₃)₂Br (0.88 mL, 7 mmol) into the mixture and stirred for another30 min. The samples were then thoroughly rinsed with DMF, followed bythe second SIP of FMA and surface characterization.

For the second SIP, 1.06 g FMA (2 mmol) was added in 10 mL DMF by drops,and commixed by magnetic bar under deoxygenating protection for 20minutes. Then CuBr (28 mg, 0.2 mmol) and pentamethyldiethylenetriamine(PMDETA, 52 mg, 0.3 mmol) were added to the solution and mixed wellresulting in a homogeneous green solution. The resulting mixture had amole ratio of monomer/CuBr/PMDETA=200/2/3. After deoxygenated for 30minutes, this mixture was then transferred to a reaction setup undernitrogen atmosphere. SIP was initiated and continued for 120 min atabout 25° C. Details of the SIP condition for monomer HEMA and MMA canbe found in a previous report (He, J., et al., Macromolecules 2007, 40,3090-3096). For in situ modification of intact microfluidic channels,reaction solutions were pumped through the channel for a desired periodof time.

X-ray Photoelectron Spectroscopy (XPS) (AXIS Ultra by Kratos Analytical,UK) was used to characterize the surface chemistry of iPDMS before andafter SIP modification. Monochromatic Al Ka X-rays (1486.7 eV) wereemployed. The X-ray source was 2 mm nominal X-ray spot size operating at15 kV and 12 mA for both survey and high-resolution spectra. Neutralizergun was on (1.85 A and 3.15 V). Survey spectra, from 0 to 1100 eVbinding energy (BE), were recorded at 160 eV pass energy with an energystep of 1.0 eV, and a dwell time of 200 ms. High-resolution spectra wererecorded at 40 eV pass energy with an energy step of 0.1 eV, and a dwelltime of 500 ms, with a typical average of 3 scans. The operatingpressure of the spectrometer was typically about 10⁻⁷ Pa. All peaks werereferenced to C 1s (CH_(x)) at 285 eV in the survey scan spectra and C1s (CH_(x)) at 284.8 eV in the deconvoluted high-resolution C 1 sspectra.

Example 2 Calculation of Surface Density of Initiator

The surface density of initiator was calculated based on the assumptionthat initiators were evenly distributed throughout the PDMS network. Thedensity of PDMS is 1.03 g mL⁻¹. It was also assumed that iPDMS had thesame density as of PDMS. For the case of 0.5iPDMS in this experiment,the volume was (10+1+0.5)/1.03=11.17 cm³, the number of initiatormolecules was N_(A)×0.5/319=9.44×10²⁰, the density was9.44×10²⁰/11.17=8.4×10⁻² chain nm⁻³. It was further assumed theinitiator had a cubic crystal structure (a=2.3 nm) and the surfacedensity was 8.4×10⁻²/2.3=3.7×10⁻² chain nm⁻². Table 2, below, shows thedensity and surface density of initiator for different iPDMS samples.

TABLE 2 0.5iPDMS 10⁻¹PDMS 10⁻²iPDMS 10⁻³iPDMS 10⁻⁶iPDMS Density 8.4 ×10⁻² 1.8 × 10⁻² 1.8 × 10⁻³ 1.8 × 10⁻⁴ 1.8 × 10⁻⁷ (chain nm⁻³) SurfaceDensity 3.7 × 10⁻² 4.7 × 10⁻³ 2.2 × 10⁻⁴ 1.0 × 10⁻⁵ 1.0 × 10⁻⁹ (chainnm⁻³) a (cubic crystal 2.3 3.8 8.3 17.8 178.2 structure parameter, nm)

Example 3 The Initiator Integrated PDMS (iPDMS): The Impact of InitiatorDensity

The initiator integrated PDMS (iPDMS) was prepared as described inExample 1. Briefly, a vinyl-terminated initiator (referred to ascomponent C, FIG. 1) was mixed with Sylgard 184 (Dow Corning), whichconsisted of liquid components A and B (Wu, Y. Z., et al., J. Am. Chem.Soc. 2007, 129, 7226-7227). The mixture was then cured at 80° C. for 2h, resulting in an elastomer. This simple mixing procedure wascompatible with replica molding, which was the key step in thefabrication of microfluidic devices. The resulting iPDMS elastomerpresented initiator molecules on the surface and was ready for furthersurface modification via SIP (FIG. 1).

The first SIP from iPDMS surfaces of varied initiator density wasconducted using monomer oligo(ethylene glycol) methacrylate (Mw=526,OEGMA). The resulting poly(OEGMA) chains had terminal hydroxyl groupsfor further functionalization. The iPDMS substrates were then treatedwith bromoisobutyryl bromide as the initiation moiety, followed by thesecond SIP using monomer 1H,1H,2H,2H-perfluorodecyl methacrylate (FMA).The resulting surface was covered with polymeric trees that had thepoly(FMA) as the branches and the poly(OEGMA) as the central trunk.After each modification step, the surfaces were characterized by XPS,SEM and contact angle of pure water. This three dimensional growth ofpolymer is referred to as the relayed SIP method.

The impact of initiator density was first tested as follows: iPDMS withfive mass ratios of A:B:C were investigated, namely, 10:1:0.5,10:1:10⁻¹, 10:1:10⁻², 10:1:10⁻³ and 10:1:10⁻⁶. From this point on, thesefive types of iPDMS are referred to as 0.5iPDMS (corresponding to asurface density of 3.7×10⁻² chain nm⁻², see Example 2 for a detailedcalculation), 10⁻¹iPDMS, 10⁻²iPDMS, 10⁻³iPDMS (surface density of1.0×10⁻⁵ chain nm⁻²) and 10⁻⁶iPDMS. For a given SIP duration of 2 hoursfor both the first and second SIP, only the 10⁻³iPDMS yieldedsuperhydrophobic surface. Thus, only representative results from twoiPDMS samples, namely 0.5iPDMS and 10⁻³iPDMS, with fixed SIP duration of2 hours for both the first and second SIP are shown and discussed.

Prior to the first SIP processes, XPS detected 0.1 atom % Br signal onthe surface of 0.5iPDMS samples, which was consistent with theinitiators evenly distributed both on the iPDMS surface and within itsbody (Wu, Y. Z., et al., J. Am. Chem. Soc. 2007, 129, 7226-7227).However, XPS indicated no detectable Br signal for the 10⁻³iPDMSsamples. This is can be attributed to the limited sensitivity of XPS asthe 10⁻³iPDMS sample did initiate polymerization from its surface, whichresulted in polymer that in turn acted as an amplification of theinitiator and was detectable by XPS (see Table 3, 10⁻³iPDMS, S4). XPSsignals of C, O, and Si for the 10⁻³iPDMS samples were reasonably closeto those for the 0.5iPDMS (Table 3). Both the 10⁻³iPDMS and 0.5iPDMS hadthe same contact angle as PDMS of about 106 degrees. Although it wasdifficult to discern the exact concentration of the initiator (componentC) on the iPDMS surface, one could reasonably assume that the amount ofinitiator integrated into the network of iPDMS was proportional to thefeed ratio of the starting components. This assumption is supported bythe following data.

FIG. 2A-F are representative SEM and contact angle images of 0.5iPDMSand 10⁻³iPDMS after the relayed SIP surface modification. Althoughdifficult to quantify, the density difference between these two samplesis apparent. The 0.5iPDMS sample was covered with entangled polymerlines (about 500 nm wide), while the 10⁻³iPDMS sample was covered withindividual dots sized from 100 to 500 nm in diameter and the height forthese dots were up to 3 μm measured by a surface profiler (FIG. 3). Thisinitiator density difference was consistent with the contact angleresults of the two iPDMS samples after the first SIP. The 0.5iPDMSsample had a contact angle at 57 degrees, which agrees well with that ofa poly(OEGMA) surface from a dense initiator surface (Ma, H. W.; Li, D.J.; Sheng, X.; Zhao, B.; Chilkoti, A. Langmuir 2006, 22, 3751-3756). The10⁻³iPDMS has a contact angle of 99 degrees, close to that of PDMS,indicating a low density coverage of poly(OEGMA) chains. Thispoly(OEGMA) density difference was further supported by XPScharacterization: the level of Br signal of the 10⁻³iPDMS and 0.5iPDMSsamples after addition of initiator moiety in S3 (FIG. 1) was 0.1 atom %and 4.6 atom %, respectively. Note the decrease of terminal Br signal inTable 3 after the first and second SIPs (0.1 atom % to 0%; or from 4.6atom % to 0.1 atom %). This was a common phenomenon in SIP and was dueto: 1) the loss of Br groups during the SIP process, and 2) the Br wasburied underneath the top polymer layer and not detected by XPS.

However, after the second run of SIP, the 10⁻³iPDMS and 0.5iPDMS sampleshad very similar surface chemistry as determined by XPS (Table 3). Thisresult was surprising as it would be expected that a higher Si signalwould result from the surface of 10⁻³iPDMS sample since most of thesurface was not covered by poly(FMA). Meanwhile, it is reasonable thatthe Si signal was greatly reduced (from 27 atom % to 0.7 atom %) for the0.5iPDMS sample as most of its surface was covered by poly(FMA) (FIG.2A). To further explore the unexpected XPS result from the 10⁻³iPDMS,the relayed SIP process was applied to a control sample of PDMS withoutinitiator and the surface chemistry characterized by XPS. The PDMSsample after the first and second SIP had a reduced Si signal (from 23atom % to 14 atom %) and increased F signal (from 0 to 23 atom %), whichwas attributed to the entrapment of monomer FMA into the PDMS networksby the minor swollen effect induced by dimethylformamide (DMF), thesolvent used in the relayed SIP process. This may be a factor in the10⁻³iPDMS sample having such a low Si signal.

Nevertheless, a superhydrophobic surface (with a static contactangle >150 degrees and sliding angle at about 1.5 degrees) was onlycreated from 10⁻³iPDMS after the second SIP, even though the 10⁻³iPDMSand 0.5iPDMS showed similar XPS results after the second SIP. The0.5iPDMS has a contact angle of 126 degrees, close to that of poly(FMA)Surface after one SIP.¹⁷ Thus, the ultra low initiator density is one ofthe key conditions (i.e., 10⁻³iPDMS but not the 10⁻⁶iPDMS, which had acontact angle at 106 degrees close to that of unmodified iPDMS, see FIG.6 for the SEM image of 10⁻⁶iPDMS after relayed SIP). Table 3, below,shows the contact angle and XPS results of the initiator integrated PDMS(iPDMS) surfaces after each step of the relayed surface-initiatedpolymerization (with oligo(ethylene glycol) methacrylate (OEGMA) and1H,1H,2H,2H-perfluorodecyl methacrylate (FMA) as the first and secondmonomer, respectively).

TABLE 3 Initiator Angle^(b) XPS^(c) (C) Status^(a) (degrees) C 1s O 1sSi 2p Br 3d F 1s 0 d S1 106 49.4 27.2 22.4 0 / S2 117 43.9 18.4 14.4 023.3 0.5 S1 106 50.4 22.8 26.7 0.1 0  S2 57 28.5 66.4 5.1 0 / S3^(e) 7463.9 16.4 9.5 4.6 / S4 126 42.1 5.8 0.7 0.1 51.3 10⁻³ S1 106 50.0 26.323.6 0 / S2 99 52.0 27.4 20.6 0 / S3 105 50.6 27.4 21.9 0.1 / S4 15541.5 5.2 0.4 0.1 52.9 ^(a)S1 stands for step 1, see FIG. 1 for details.^(b)Average values from 3 different locations, SE <± 3 degrees. ^(c)Atom% was based on the survey scan of Br 3d (71 eV), Si 2p (102 eV), C 1s(285 eV), O 1s (532 eV), and F 1s (690 eV). Average values from 3different locations, SE <± 0.4 eV, d Sample was PDMS. ^(e)Sample had5.6% N 1s (399 eV) due to Et₃N, which was used as catalyst in the S3.

The relayed SIP strategy is required to generate the superhydrophobicityon iPDMS. A control experiment was conducted using SIP and FMA on0.5iPDMS surface (FIG. 2G-I). After 4 hours of SIP, the surface wascovered with individual dots similar to that in FIGS. 2D and 1E but withsmaller size, and was not superhydrophobic. Longer SIP duration (up to 8hours) resulted in similar surface morphology and contact angles, whichwas attributed to the difficulties in running SIP for longer duration(He, J., et al., Macromolecules 2007, 40, 3090-3096). In the relayed SIPprocess, the first SIP prepared a post to support the second SIP, whichwas a vertical direction growth. The second SIP provided an effectiveway to realized lateral expansion. The duration of the first and secondSIP was, however, not critical as long as a decent (>200 nm laterallyand >1000 nm vertically) tree-size was achieved.

The duration of the first and second SIP was varied from 1 hour to 8hours for all the five iPDMS samples. It was observed that the surfacemorphology was very diverse, although no conversion from a hydrophobicsurface to a superhydrophobic surface was observed. For example, FIG.4B, FIG. 2B and FIG. 4D show SEM images for the 0.5iPDMS samples afterthe first SIP with different durations of 1 h, 2 h and 4 h,respectively. Although the morphology was different, all had a similarcontact angle of 126 degrees or 130 degrees. In addition, comparing FIG.2E with FIG. 4F, the density of poly(OEGMA-FMA) trees increased as thesecond SIP duration increased from 2 h to 6 h. However, these 10⁻³iPDMSsamples also shared similar contact angles at 150 degrees and 155degrees. Thus, the effect of the SIP duration on the contact angles ofwater is limited.

Example 4 Comparison of Methyl Methacrylate (MMA), OEGMA, andHydroxyethyl Methacrylate (HEMA), as the Monomer to Replace FMA

The monomer FMA applied in the second SIP process was also critical inpreparing superhydrophobic iPDMS surfaces when compared to methylmethacrylate (MMA), OEGMA, and hydroxyethyl methacrylate (HEMA) as thesecond polymer layer. FMA acted both by lowering the surface energy withpoly(FMA) and by generating a surface morphology with hierarchical scaleroughness. For comparison, three other monomers were used, namely,methyl methacrylate (MMA), OEGMA, and hydroxyethyl methacrylate (HEMA),as the monomer to replace FMA in the second SIP process while theconditions for S1 to S3 were maintained the same as before (FIG. 5).Previously the contact angles of surfaces with poly(MMA), poly(HEMA) andpoly(OEGMA) polymer brushes were reported at 70 degrees, 47 degrees(Shah, R. R., et al., Macromolecules 2000, 33, 597-605) and about 57degrees (Ma, H. W.; Li, D. J.; Sheng, X.; Zhao, B.; Chilkoti, A.Langmuir 2006, 22, 3751-3756), respectively. We had the contact anglesfor the 0.5iPDMS samples covered with poly(MMA), poly(HEMA) andpoly(OEGMA) at 85 degrees, 39 degrees and 48 degrees, respectively,which were all close to the previous reports.

The patterns (or wrinkles) shown in FIGS. 5A, 4C and 4D were unexpectedand different from that in FIG. 2A. The exact mechanism behind thepattern formation was not clear although a possible explanation lies inthat the mechanical stress induced by the tethered polymers might play akey role in pattern formation: different monomers resulted in distinctlydifferent surface morphology (or wrinkle) for the 0.5iPDMS samples.These differences in surface morphology may cause the unique behavior ofSi signal detected by XPS after the relayed SIP.

For example, with HEMA as the monomer in the second polymerization step,the surface of 10⁻³iPDMS sample should have a lower surface coverage ofpoly(HEMA) than the surface of 0.5iPDMS sample but XPS showed a similarSi signal for these two samples: 10.7% and 11.8%, respectively. This canbe attributed to the fact that the 0.5iPDMS sample showed a roughersurface morphology than the 10⁻³iPDMS sample, which led to more area ofthe PDMS surface exposed to XPS detection, thus resulting in an increaseof Si signal.

The 10⁻³iPDMS sample covered with poly(MMA) had a contact angle of 82degrees, close to that of 0.5iPDMS sample. However, a significantcontact angle increase was observed for the 10⁻³iPDMS samples coveredwith poly(HEMA) and poly(OEGMA) at 67 degrees and 72 degrees,respectively. The hydrophilicity of these three samples indicated theconsequence of the surface chemistry resulting from FMA. The monomer FMAis also unique in that the 10⁻³iPDMS samples with FMA as the secondmonomer (FIG. 2E) having a different surface morphology from the10⁻³iPDMS samples with the other three tested monomers (FIG. 5B forHEMA). The surface of MMA and OEGMA were also featureless (data notshown). Table 4, below, shows the contact angle and XPS results of theinitiator integrated PDMS (iPDMS) surfaces with different monomers inthe second surface-initiated polymerization (SIP) process.

TABLE 4 Initiator Angle ^(a) XPS ^(b) Monomer (C) (degrees) C 1s O 1s Si2p F 1s None ^(c)   0.5 ^(d) 106 50.4 22.8 26.7 / 10⁻³ 106 50.0 26.423.6 / FMA 0.5 126 42.1 5.8 0.7 51.3 10⁻³ 155 41.5 5.2 0.4 52.9 MMA 0.585 58.7 24.5 16.8 / 10⁻³ 82 63.4 24.9 11.7 / OEGMA 0.5 48 59.2 28.9 11.9/ 10⁻³ 72 60.5 30.8 8.7 / HEMA 0.5 39 61.2 27.0 11.8 / 10⁻³ 67 61.4 28.210.7 / ^(a) Average values from 3 different locations, SE <± 3 degrees.^(b) Atom % was based on the survey scan of Si 2p (102 eV), C 1s (285eV), O 1s (532 eV), and F is (690 eV). Average values from 3 differentlocations, SE <± 0.4 eV. ^(c) Sample was iPDMS before the first SIPprocess. ^(d) Sample had Br 3d (71 eV) intensity at 0.1 atom %.

EQUIVALENTS

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended as singleillustrations of individual aspects of. Many modifications andvariations can be made without departing from its spirit and scope, aswill be apparent to those skilled in the art. Functionally equivalentmethods and apparatuses within the scope of the disclosure, in additionto those enumerated herein, will be apparent to those skilled in the artfrom the foregoing descriptions. Such modifications and variations areintended to fall within the scope of the appended claims. The presentdisclosure is to be limited only by the terms of the appended claims,along with the full scope of equivalents to which such claims areentitled. It is to be understood that this disclosure is not limited toparticular methods, reagents, compounds compositions or biologicalsystems, which can, of course, vary. It is also to be understood thatthe terminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember. Thus, for example, a group having 1-3 cells refers to groupshaving 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers togroups having 1, 2, 3, 4, or 5 cells, and so forth.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. An article comprising a hydrophobic coatinghaving a contact angle of at least about 150 degrees, wherein thecoating comprises: a polymer substrate comprising poly(dimethyl)siloxane (PDMS) and a first linker incorporated therein at a specifiedsurface density of from about 3×10⁻⁴ to about 9×10⁻⁸ units per nm²; afirst polymer layer in contact with said first linker; a second linkerin contact with said first polymer layer; and a second polymer layer incontact with said second linker; wherein the article is selected fromthe group consisting of a microfluidic device, wherein the microfluidicdevice comprises at least one channel disposed thereon, a lab-on-a-chip,a boat, and a marine monitoring device.
 2. The article of claim 1wherein the article is protein resistant.
 3. The article of claim 1wherein the article is marine antifoulable.
 4. The article of claim 1,wherein the first polymer layer is bonded to the first linker by acarbon-carbon bond.
 5. The article of claim 1, wherein the second linkeris bonded to the first polymer layer by an ester bond.
 6. The article ofclaim 1, wherein the second polymer layer is bonded to the second linkerby a carbon-carbon bond.
 7. The article of claim 1, wherein the firstlinker comprises an alkyl group with a terminal functional group.
 8. Thearticle of claim 1, wherein the first linker comprises a linear (C6-C12)alkyl group with a terminal alpha-haloester group.
 9. The article ofclaim 1, wherein the first polymer layer comprises polyethylene glycol.10. The article of claim 1, wherein the second linker comprises acarbonyl group.
 11. The article of claim 1, wherein the second polymerlayer comprises fluorine.
 12. A microfluidic device comprising: at leastone channel disposed thereon; and a hydrophobic coating having a contactangle of at least about 150 degrees, wherein the coating comprises: apolymer substrate comprising poly(dimethyl) siloxane (PDMS) and a firstlinker incorporated therein at a specified surface density of from about3×10⁻⁴ to about 9×10⁻⁸ units per nm²; a first polymer layer in contactwith said first linker; a second linker in contact with said firstpolymer layer; and a second polymer layer in contact with said secondlinker.
 13. A method for making a hydrophobic coating having a contactangle of at least about 150 degrees, said method comprising: 1)polymerizing a mixture comprising a poly(dimethyl-methylvinylsiloxane)prepolymer, poly(dimethyl-methylhydrogensiloxane) precursors andundec-10-enyl-2-bromo-2-methylpropanoate, under thermal conditions toform a polymer substrate; 2) contacting oligo(ethylene glycol)methacrylate with said polymer substrate under first polymerizingconditions to provide a first polymer layer bound to the polymersubstrate through the undec-10-enyl-2-bromo-2-methylpropanoate; 3)contacting 2-bromoisobutyryl bromide with said first polymer layer underreaction conditions to provide a reactive surface; and 4) contacting 1H,1H, 2H, 2H-perfluorodecyl methacrylate with said reactive surface undersecond polymerizing conditions to provide the hydrophobic coating. 14.The method of claim 13, wherein the first polymerizing conditionscomprise metal catalyzed polymerization.
 15. The method of claim 13,wherein the second polymerizing conditions comprise metal catalyzedpolymerization.
 16. The method of claim 13, wherein the ratio ofpoly(dimethyl-methylvinylsiloxane) prepolymer,andpoly(dimethyl-methylhydrogensiloxane) precursors toundec-10-enyl-2-bromo2-methylpropanoate is about 10:1:10⁻³.
 17. Themethod of claim 13, wherein the surface density ofundec-10-enyl-2-bromo-2-methylpropanoate is about 1.0×10⁻⁵ units pernm².
 18. The method of claim 13, wherein the first polymerizingconditions comprise heating the monomer and linker to a temperature offrom about 25° C. to about 90° C.
 19. The method of claim 13, whereinthe reaction conditions comprise acetylation conditions.
 20. The methodof claim 13, wherein the second polymerizing conditions comprise heatingthe monomers to about 80° C.